Operando XRD: a practical guide
How to follow a battery material by X-ray diffraction while it is cycling: what operando means, which geometry and window to choose, and how to plan the experiment.
Ex situ, in situ, operando: what is the difference?
All three use X-ray diffraction to look at the crystal structure of an electrode material. They differ in where the material is, and what it is doing, when it is measured.
Outside the cell
The cell is stopped and opened, and the electrode is measured on its own. It is simple, but the material can relax or react with air before it is measured, and every state of charge needs a new cell.
Inside the cell, at rest
The electrode stays in the cell, and the current is usually interrupted during each measurement. One cell gives the whole series, but the material is at rest when it is measured.
Inside the cell, while it works
Patterns are collected continuously while the current flows. You see the material as it works, including short-lived intermediate phases and differences between charge and discharge.
What operando data looks like
Each line in the figure is one diffraction pattern. Stacked in time order next to the voltage curve, the patterns show how the structure changes as the cell is charged and discharged.
- A peak that shifts continuouslyThe lattice expands or contracts within a single phase: a solid-solution reaction.
- One set of peaks fades while another growsTwo phases coexist and one converts into the other: a two-phase reaction, usually seen as a voltage plateau.
- New peaks appearA new phase has formed. If it disappears again later, it is an intermediate that an ex situ measurement could miss.
- Peaks get broaderStrain, smaller crystalline domains or a loss of crystallinity.
Reflection or transmission?
The two geometries do not look at the same part of the electrode, and they do not suit the same instruments.
| Reflection | Transmission | |
|---|---|---|
| Beam path | The beam enters through the window and is diffracted back by the electrode lying behind it. | The beam passes through the whole cell. |
| What you probe | The part of the electrode closest to the window. | The full thickness of the electrode, together with every other layer in the beam. |
| Typical instruments | Standard θ-θ laboratory diffractometers, and synchrotron beamlines. | Synchrotron beamlines, and laboratory diffractometers equipped for transmission. |
| Watch out for | A change in sample height shifts the peaks. In a thick electrode, the surface may not react exactly like the bulk. | Every component crossed by the beam absorbs X-rays and may add its own peaks. |
| A good fit for | Most powder electrodes on a laboratory instrument. | Tape-cast electrodes, full cells and solid-state batteries. |
| Our cell | HexaCell Reflection | HexaCell Transmission HexaCell Small Beam |
Choosing the window
The window has to let X-rays through while keeping the cell sealed. Its material matters for both the diffraction pattern and the electrochemistry.
A window that conducts electricity
Beryllium, aluminium and glassy carbon are all good electrical conductors. This is an important point: some operando cells use windows made of Kapton or glass, which do not conduct electricity, and this can alter the electrochemistry of the electrode behind the window.
The right window depends on your wavelength
What separates the three materials is how much of the beam they absorb, and absorption depends strongly on the wavelength. With the copper radiation used by most laboratory diffractometers, only beryllium lets enough of the beam through. Aluminium and glassy carbon would absorb so much that no usable signal would reach the detector. At shorter wavelengths (higher energy), such as molybdenum radiation or a synchrotron beam, their absorption becomes acceptable and all three can be used.
| Beryllium | Aluminium | Glassy carbon | |
|---|---|---|---|
| Copper radiation most laboratory diffractometers |
Yes — very low absorption | No — absorbs too much | No — absorbs too much |
| Molybdenum radiation or synchrotron shorter wavelength |
Yes | Yes | Yes |
| Diffraction peaks from the window | Yes | Yes | No sharp peaks |
| Electrical conductor | Yes | Yes | Yes |
Beryllium
Very low absorption, even with copper radiation: the window of choice for a laboratory diffractometer with a copper tube. It adds its own diffraction peaks to the pattern. Handle it with care: beryllium dust is toxic, and the metal can corrode at high positive potentials.
Aluminium
A cost-effective, robust window for shorter wavelengths: molybdenum radiation or a synchrotron beam. It adds its own diffraction peaks to the pattern.
Glassy carbon
Also for shorter wavelengths. It gives no sharp diffraction peaks of its own, which suits measurements requiring low background scattering.
Not sure which one fits your instrument, material and voltage range? Ask us.
Laboratory or synchrotron?
Available every day
No proposal, no travel, and no limit on how long the experiment runs: ideal for screening materials, developing a method, and following slow cycling over several days. A pattern typically takes minutes, so the cycling rate has to be chosen accordingly.
Fast and highly resolved
The intensity of the beam brings the time per pattern down to seconds or less, with high angular resolution. It is the choice for fast cycling, weak reflections, small beams, and subtle structural changes. Beamtime is limited, so the experiment has to work the first time.
The two are complementary: an experiment prepared and tested on a laboratory instrument is far more likely to succeed at the beamline.
Seven things to get right before you start
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Match the scan time to the cycling rate
The composition changes during each scan by about C-rate × scan time (in hours). At C/10 with a 30-minute scan, that is 0.05 per pattern, or 20 patterns per charge. If a scan takes too long, the material changes while it is being measured and the peaks smear.
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Measure only the angular range you need
Restricting the scan to the reflections that matter shortens each pattern and improves the time resolution.
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Check the electrochemistry first
The capacity and voltage profile in the operando cell should match what you get in your usual test cell. If they do not, solve that before measuring.
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Keep the electrode flat and in contact with the window
In reflection, a change in sample height shifts the peaks. A flat, well-pressed electrode limits it, and a peak from the window can serve as an internal reference.
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Record a pattern before applying any current
It is your reference for the pristine material, and a last check of the alignment and of the cell.
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Synchronise the clocks
Start the diffractometer and the potentiostat from the same time reference, and note the start time of every scan, so that each pattern can be matched to a voltage.
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At the synchrotron, mind the beam
An intense beam can alter the reaction where it hits the electrode. Limit the exposure, or move the beam between positions, and compare with the electrochemistry of the whole cell.
Frequently asked questions
What is the difference between in situ and operando XRD?
In both cases the electrode is measured inside the cell. In situ usually means that the current is interrupted while each pattern is recorded, so the material is at rest. Operando means that the patterns are recorded continuously while the cell is charging or discharging.
Can I do operando XRD on a laboratory diffractometer?
Yes. A reflection cell such as the HexaCell Reflection fits standard θ-θ laboratory diffractometers. A laboratory source is less intense than a synchrotron, so each pattern takes longer and the cycling rate has to be slower.
Reflection or transmission: which should I choose?
Reflection suits most powder electrodes on a standard laboratory diffractometer, and probes the part of the electrode closest to the window. Transmission probes the full thickness of the electrode and suits tape-cast electrodes, full cells and solid-state batteries; it needs a synchrotron beamline or a laboratory instrument equipped for transmission.
Which window material should I use?
It depends on your wavelength. With copper radiation, used by most laboratory diffractometers, choose beryllium: its absorption is very low, whereas aluminium and glassy carbon would absorb too much of the beam. With a shorter wavelength, such as molybdenum radiation or a synchrotron beam, aluminium and glassy carbon can be used as well. Beryllium and aluminium add their own diffraction peaks to the pattern; glassy carbon gives no sharp peaks. All three are good electrical conductors, unlike the Kapton or glass windows of some cells, which can alter the electrochemistry. Contact us if you are unsure.
How long should each diffraction pattern take?
Short enough that the material barely changes during one scan. The composition changes by about C-rate × scan time in hours: at C/10, a 30-minute scan corresponds to 0.05 per pattern, or 20 patterns per charge.
What is the Leriche cell?
The Leriche cell is an electrochemical cell for operando X-ray studies of battery materials, first described by Leriche et al. in 2010. Its second version, the LeRiChe'S Cell v2, was described in 2023. The HexaCell made by Insight Instruments is its commercial version.
References
- J.-B. Leriche, S. Hamelet, J. Shu et al., “An electrochemical cell for operando study of lithium batteries using synchrotron radiation”, J. Electrochem. Soc. 157, A606 (2010). doi:10.1149/1.3355977
- K. Choudhary, I. O. Santos Mendoza, A. Nadeina et al., “Operando X-ray diffraction in transmission geometry ‘at home’ from tape casted electrodes to all-solid-state battery”, J. Power Sources 553, 232270 (2023). doi:10.1016/j.jpowsour.2022.232270
Planning an operando experiment?
Tell us about your instrument and your material: we will help you choose the cell, the window and the holder.